Process for the upgrading of hydrocarbons by hydrogen-donor diluent cracking



NOV 27, 1956 H. z. MARTIN 2,772,218

PROCESS FOR THE UPGRADING OF HYDROCARBONS BY HYDROGEN-DONOR DILUENTCRACKING Filed DSC. 8, 1955 3 1 Homer Z.Marfnfinvenfor M2M/AttorneyUnited States Patent O PROCESS FOR THE UPGRADING OF HYDRO- CARBONS BYHYDROGEN-DONOR DILU- ENT CRACKENG Homer Z. Martin, Cranford, N. J.,assigner to Esso Research and Engineering Company, a corporation ofDelaware Application December 8, 1953, Serial No. 396,968

4 Claims. (Cl. 196--50) The present invention relates to the conversionof residual oil fractions and particularly to a process and a system forconverting residual oils such as reduced crude petroleum to morevolatile products by the thermal cracking of the oils in the presence ofa hydrogen donor diluent.

Hydrogen donor diluent cracking (HDDC) has been previously proposed. Thepurpose in donor diluent cracking is to cause hydrogen retained by thediluent to transfer to the heavier residual fractions being cracked andin this way to prevent the formation of coke which is the usual productof ordinary thermal cracking or coking operations. |The HDDC process ismore fully illustrated by co-pending application, Upgrading ofHydrocarbon Oils, S. N. 365,335, tiled July l, 1953, now abandoned, byArthur W. Langer, lr. The hydrogen donor method offers a possibility ofincreasing the liquid yield over that attainable from the ordinarycoking processes. A difficulty with the hydrogen donor process is thatin normal refinery operations the quantity of naphthenic streamssuitable for hydrogen transfer is limited. ln fact, it is not easy toiind enough suitable aromatic streams which can be hydrogenated to serveas hydrogen donors. For this reason, the previously proposed processeshave utilized the standard recycling of streams method to obtain enoughmaterial suitable for hydrogenation.

The previous schemes, however, embody recycling of various boiling rangecuts which are not entirely suitable for the purpose of hydrogenationand the consequent hydrogen transfer operation. That is, the proposedstreams do not contain a high enough proportion of suitable aromatics toact as hydrogen carriers. Hence, when the thermal operation takes placesome of the residuum is left unaltered. Another diiculty with pastschemes is that one of the products of the operation is usually intendedfor use as feed for catalytic cracking. Very often vthe material whichis used for rehydrogenation, to form a hydrogen donor, is identicalywith that which is put out as product for catalytic cracking. 'I'heserequirements are somewhat contradictory since the raw material forhydrogen donor production is desired to be predominantly aromatic, whilethe catalytic cracking feed stock is preferably predominantlynon-aromatic.

This invention is based upon the discovery that both these difficultiescan be obviated by incorporating into the process a suitable step ofaromatic separation. The separated aromatics or predominantly aromaticconstituents are used for rehydrogenation while the aromaticpoor productis sent to the catalytic cracking operation or to other operations usinggas oils and similar products. It will be appreciated that by thisextraction step, i. e., concentration of desirable aromatics in thehydrogen donor diluent, there will be a marked improvement in thequality of the products from the HDDC system. This improvement resultsfrom two factors. First, because of the improved quality of the hydrogendonor Vdiluent charged to the HDDC system, there willbe less thermaldegradation of the heavy residual fractions being cracked.-

2 Second, and of equal importance, the catalytic cracking feed stockproduced will be greatly improved by elimination of the aromatics.Formerly, removal `of aromatics from catalytic feed stocks was notattractive because no use existed for the extracted aromatics. Thisinvention, however, makes novel and desirable use of aromatics removedfrom catalytic cracking feed stocks. The process of this invention isillustrated diagrammatically in the attached drawing which forms a partof this specification.

A primary object of the present invention is to make it possible toconvert all, or substantially all, of even the heaviest hydrocarbon oilsand the most refractory to lower boiling or lighter, and hence morevaluable, hydrocarbon products. Another object is to improve greatly thequality of the products produced by hydrogen donor diluent cracking ofheavy hydrocarbon oils. A further object is to reduce substantially theproduction of coke when heavy residua are thermally cracked and toapproach percent conversion of the residua to useful gas oils. Theinvention aims particularly for the increased production of gas oil.This gas oil may be used as heating fuel, diesel fuel or fuel oil but isintended to be used primarily as catalytic cracking feed stock. A morespecific object of this invention is to increase the efficiency andpracticability of the hydrogen donor process by incorporating into thatprocess a step of aromatic separation. Further objects and advantageswill appear more clearly as this description proceeds.

Generally stated, the objects of this invention areobtained by mixing aheavy residuum feed with a recycled partially hydrogenated thermal tarrich in selected aromatics. The mixture is then heated and passedthrough a thermal cra-cking and soaking zone. After allowing a suitabletime for conversion, the mixture is separated -by fractionationessentially into lighter hydrocarbons, gas oils, a diluent fraction anda heavy bottoms fraction. The diluent fraction is used as a source ofaromatics for the hydrogen donor diluent. It is possible, however, touse all or part of the bottoms fraction as a source of these aromatics.If so, then it would not be necessary to make a diluent cut. The diluentfraction or a portion thereof is transferred to an aromatic extractionor separation Zone where a suitable selection of aromatics is made. Theselected aromatics are then partially hydrogenated by conventional meansto yield the donor diluent. 'Ihe process is capable of many variationswhich will appear below as the embodiment illustrated in the drawing isdescribed in detail.

The prior art has suggested that various hydrogenated aromatic chemicalsmay have utility as hydrogen carriers for processes like the HDDC. Theprior art has mistakenly supposed, however, that the more highlyhydrogenated materials are superior. Recently this has -been found to bean erroneous and unwarranted assumption. A heavy oil fraction, boilingabove 500 F. up to about 1100 F., containing substantial and preferablyat least major portions of condensed ring aromatics and having addedthereto some easily removable hydrogen atoms, but not enough to approachsaturation, shows outstanding utility as hydrogen donor material. Themore highly hydrogenated aromatics show much less activity. Moreover,pure or substantially pure chemical compounds or hydrogenated productsderived from pure compounds are usually relatively very expensive andtheir use as hydrogen donor diluents is not economically justifiable.

It has been discovered that there are some highly aromatic condensedring fractions available in most crude oils, and especially in heavyresidua, so that'the feed stocks themselves usually can supply a majorproportion of the required diluent.- Relinery streams which arerich inhigh boiling easily condensed aromatics may'- be partially hydrogenatedby adding thereto 'from about 200 Patented Nov. 27, 1956 to 2000 s. c.f. ofhydrogen per barrel of diluent. These streams will make excellentdiluents. Thermal tars boiling` in the range of 700 to 900 E. areparticularly preferred. Thus, cycle stock fractions or catalytic feedstocks may be used asa source of donor material without special thermalcracking. This type of material is particularly desired because they areusually surplusage in renery'operations and are, therefore, a cheapsource for the donor diluent.

In general, the condensed ring aroma-tics that are selected for partialhydrogenation .are those which` are quite stable to cracking under thereaction conditions. They are susceptible to relatively easyhydrogenation and dehydrogenaition. Complete hydrogenation produces amuch less effective donor. Ordinarily it is preferred to recycle a 700to 900 F. cut of .a thermal tar, i. e. a thermally cracked cycle oilfrom catalytic cracking bottoms, after its partial hydrogenation. Bythis method a diluent material can -be used over and over as llong asits aromatic structure is not changed. Usually however the recycled cutsdo not contain la suliiciently high percentage of condensed ringcompounds to accomplish effectively the task of hydrogen donation. Thisinvention. proposes that thenmal tars of the type mentioned above usedas hydrogen donor material can be made much more effective by suitablearomatic extraction, and thus concentration of the aromatic donormaterial. The process of -this invention is capable of using any one ofseveral well-known aromatic extraction or concentration processes.

To make the invention -more clear the attached drawing will now bediscussed in detail.

The residuum feed enters the process through line and is mixed with therecycled hydrogenated -thermal tar supplied by line 11. Recycled heavybottoms from the fractionation stage can also be mixed with the feed atthis point, either through a separate line or through the thermal .tarline. A preferred embodiment of the invention is to recycle theunconverted bottoms from the 'frac-A tionation stage. The recycled'bottoms will amount preferably to about 0.5 to 2.0 volumes -of bottomsper volume of feed and the hydrogenated tar will amount to 0.5 to 1.0volumes per volume of feed. Of course, depending. upon the type of feed,operating conditions, degree of hydrogenation and like factors, therecycled hydrogenated tar could vary anywhere from 0.1 to 2.0 volumes oftar per volume of feed. The mixture is then passed to a thermal crackingzone. Any suitable type of equipment could be used :but for the purposeof this illustration a coil and drum arrangement is depicted. Themixture is heated in the furnace 1 and passed -by line 12 to the soaker2 where -it remains for a suitable time. The conditions for cracking inextreme cases may vary from temperatures of 500 to 1200 F., pressures of100 to 3000 p. s. i. g. and resi-dence times of 0.1 to 5.0 v./v./hr.,but for a topped virgin crude feed, 800 to 850 F., 300 to 400 p. s. i.g. and l to 3 v./v./hr. are preferred. I-t is understood, of course,that residence time in part, is a function of the cracking temperature.

After this treatment, the cracked mixture is transferred, via line 13,to a fractionator 3 (or a flashing chamber or is partial-ly condensed)in order that the ylighter gas oils and gasolines can be separated fromthe heavy unconverted residuum and the donor material. As lshown in thedrawing, the cracked material is divided into four components. Gas isremoved by line 14, a gas oil fraction by line as product, 'a diluentcut by line 16 and the bottoms `by line 17. The diluent cut can have awide variation in boiling range, say from 400 to 1l00 F., depending uponthe processed material and operating conditions, but a 700 to 900 F.,range is preferred. A diluent cu-t need not be made at all. Instead, allor part of.. the bottoms. @aube Sent to an aromatic extraction. unit to,be described.

Several; variations in. thev new can, ybe. made at this point. As justmentioned the bottoms can be transferred by lines 17, 27, 18 and 16a, tothe aromatic extraction unit, all or part 4can be recycled by line 25lto the fee-d, or part can by-pass the extraction unit by lines 27 and26 to the liydrogenator 6. The same is true of the diluent cut, if onebe made. All or part of it carried by lines 16 and 16a, can be used asthe source of aromatics, can be hydrogenated by passing it to thehydrogenator 6 via lines 16, 18 and 26, or can be recycled by line 16,18, 27 and 2S to the feed.

Because the aim of this invention is to maintain an aromatic level inthe hydrogenate-d tar, only a portion of the diluent .cut or bottomsneed be used as a feed to the aromatic extraction plant. For a toppedvirgin crude feed, the amount of a 700-900 F. diluent cut sent toextraction will amount to 0.6 to 1.5 volume of cut per volume of feed.For the same feed, lthe recycled bottoms to the feed will amount toabout 1 volume of bottoms per volume of feed and about 0.5 to 1 volumeof 700-900 F. cut will be passed directly to the hydrogenator.

As mentioned, it is possible to use a variety of aromatic separationplants or processes using extraction media such as sulfur dioxide,antimony trichlofride :and furfural. For the purpose of illustration asimplified phenol extraction system is used. The diluent cut feedVenters the extracting column 4 by line 16a and is mixed with recycledphenol supplied by line 20. The raffinate is removed by line 19. to`stripping tower 7 where the phenol is separated and returned by line 30and the aromaticpoor oil is removed by line 29 as product of theprocess. The extract leaves column 4 by line 21 and goes to a stripper 5where :the phenol is separated and returned by line 20 and thearomatic-rich oil is removed and passed by line 22l to thehy'drogenator, the hydrogenator being supplied with hydrogen from anexternal source by line 23.

The thermal tar diluent is hydrogenated by adding to the diluent about200 'to 6000 cubic feet of hydrogen per barrel ofthe diluent and passingthe mixture over a suitable hydrogenation catalyst. Since there arelikely to be appreciable quantities of sulfur present in the diluent, itis usually preferable to employ a relatively sulfur insensitivecatalyst, such as molybdenum sulfide o-r a `tungsten nickel sulfide, asis well known in the art. Conventional hydrogenation pressures, e. ig.to 1000 p. s. i. g. or more with conventional temperatures may be used.The condi-tions, in any case, should be so chosen that the diluent isonly partially hydrogenated. The diluent should pick up enough easilyremovable hydrogen to be effective as a donor, but not enough toapproach saturation or to convertit substantially to a naphthene. With700 to 900 F. thermal tar of average molecular weight around 300 or so,hydrogen consumption may run from about 250 to 1000 s. c. f. per barrel.The consumption of hydrogen may vary considerably, however, from aslittle as 100 to as much as 2,000 or more s. c. f./bbl. The importantcriterion is that the hydrogenation be carried approximately to thatstage at which hydrogen transfer, in` the thermal operation, to lthecracked products reaches a maximum. After being hydrogenated, `thediluent is passed by lines 24 and 11 to the feed.

Since the materials are recycled, it may be necessary to provide for apurge and make-up to prevent the excessive build-up of contaminants,like metals and ash, in the recycled streams. For this reason a purgeline 28 is indicated in the recycled bottoms line 17 and a make-up line31a is shown for the recycled diluent line. Line 31b may be used to addmake-up diluent to the extraction column 4. By adding make-up diluentthrough line Slb the load on the hydrogenator 6 can be reduced since ithandles a diluent higher in the desired aromatics and consequently wouldhandle a lesser amount of diluent. This fresh make-up diluent can,consist of any refinery stream that contains suitable proportions ofaromatics. Thermal tar boiling in the, range of 700-900 F. from acatalyticv cracking unit is particularly suitable but other suitablematerials are lube oil extracts, clarified oil, tars and asphalts fromthe deasphalting of residua, and the like.

For the described process, the following material balance could beexpected for a feed stock having the following specifications: 8 APIgravity, 2l wt. percent Conradson carbon, 1000 F. initial boiling point:

Having described a preferred embodiment of the invention, it is to beunderstood that the invention is not to be limited by the descriptionbut only by the following claims.

What is claimed is:

1. In a process for upgrading heavy hydrocarbonaceous oils whichcomprises the steps of partially hydrogenating in a hydrogenation zone arecycled hydrocarbon stream obtained as hereinafter described to form ahydrogen donor diluent, admixing said donor diluent with a heavy oilfeed and a recycled bottoms fraction, thermally cracking the resultingmixture, and separating the cracked mixture into at least a lightfraction as product, a diluent fraction boiling between about 700 and900 F. and a bottoms fraction; the improvement which comprises passingat least a portion of said diluent fraction to an aro matic separationzone, separating from said portion of diluent fraction a concentratecontaining substantially increased proportions of condensed ringaromatics by selective solvent treatment and passing said concentrate tosaid hydrogenation zone to supply at least a portion of said recycledhydrocarbon stream.

2. The process of upgrading heavy hydrocarbons which comprises mixing aheavy hydrocarbon feed with a partially hydrogenated hydrogen donordiluent including a high boiling cycle stock from catalytic cracking ofgas oil, subjecting the mixture to :conditions conducive to thermalcracking in the absence of catalyst and free hydrogen, separating fromthe thermally treated mixture a relatively heavy distillate fraction,separating from at least a portion of said heavy distillate fraction inan aromatic extraction zone a hydrocarbon stream containing substantialproportions of aromatics, partially but not completely hydrogenatingsaid hydrocarbon stream in a hydrogenation zone in the presence of asulfur resistant catalyst and recycling and blending the hydrocarbonstream so hydrogenated to supply at least a portion of said hydrogendonor diluent.

3. The process of claim 2 which comprises admixing said hydrogen donordiluent with said feed in proportions of 0.1 to 2 vols. of diluent/vol.of feed, when said heavy distillate fraction boils in a range above 700F. and when about to 2000 s. c. f. of hydrogen/bbl. of said hydrocarbonstream is added in said hydrogenation zone.

4. In a hydrogen donor diluent conversion process wherein a heavy oil isthermally cracked in the absence of the catalyst and free hydrogen, inadmixture with a hydrogen donor diluent, wherein spent hydrogen donordiluent is recovered and regenerated by partial hydrogenation andrecycled, the improvement which comprises subjecting at least a part ofsaid spent hydrogen donor diluent to an aromatic separation step toconcentrate the desirable aromatic polycyclic ring structures thereinand thereafter hydrogenating said concentrate by adding thereto 250 to1000 s. c. f. per barrel of hydrogen in the presence of an activehydrogenation catalyst whereby the effective aromaticity and thehydrogen donor properties of the diluent are substantially improved.

References Cited inthe le of this patent UNITED STATES PATENTS 2,363,782Frey Nov. 28, 1944 2,367,474 Stewart Jan. 16, 1945 2,426,929Greensfelder Sept. 2, 1947 2,620,293 Blue et al. Dec. 2, 1952 2,701,783Long Feb. 8, 1955 OTHER REFERENCES Sachanen: Chemical Constituents ofPetroleum, page 229 (1945), Reinhold Publishing Co., New York.

1. IN A PROCESS FOR UPGRADING HEAVY HYDROCARBONACEOUS OILS WHICHCOMPRISES THE STEPS OF PARTIALLY HYDROGENERATING IN A HYDROGENATION ZONEA RECYCLED HYDROCARBON STREAM OBTAINED AS HEREINAFTER DESCRIBED TO FORMA HYDROGEN DONOR DILUENT, ADMIXING SAID DONOR DILUENT WITH A HEAVY OILFEED AND A RECYCLED BOTTOMS FRACTION, THERMALLY CRACKING THE RESULTINGMIXTURE, AND SEPARATING THE CRACKED MIXTURE INTO AT LEAST A LIGHTFRACTION AS PRODUCT, A DILUENT FRACTION BOILING BETWEEN ABOUT 700* AND900* F. AND A BOTTOMS FRACTION; THE IMPROVEMENT WHICH COMPRISES PASSINGAT LEAST A PORTION OF SAID DILUENT FRACTION TO AN AROMATIC SEPARATIONZONE, SEPARATING FROM SAID PORTION OF DILUENT FRACTION A CONCENTRATECONTAINING SUBSTANTIALLY INCREASED PROPORTIONS OF CONDENSED RINGAROMATICS BY SELECTIVE SOLVENT TREATMENT AND PASSING SAID CONCENTRATE TOSAID HYDROGENATION ZONE TO SUPPLY AT LEAST A PORTION OF SAID RECYCLEDHYDROCARBON STREAM.